1. Field of the Invention
The present invention relates to an injection-locked frequency divider. More particularly, the present invention relates to an injection-locked frequency divider with an increased locking range by the use of a feedback action of transformers.
2. Description of Related Art
Frequency dividers have been widely applied in mixed signal integrated circuits, for example, crucial elements of multiplexers, phase locked loops, and frequency synthesizers. In recent years, in response to the requirements of consumers and the changes of systems technologies, an injection-locked frequency divider from among various kinds of frequency dividers attracts more attention due to its applicability in the operation of a high-speed system.
FIG. 1 is a schematic structural view of a conventional injection-locked frequency divider. Referring to FIG. 1, the conventional injection-locked frequency divider 100 is constructed by an LC-tank oscillator 110 and a signal injection unit 120. The signal injection unit 120 receives an injection signal SIN1. The LC-tank oscillator 110 adjusts its oscillation frequency through a reactance control signal SIP1. When the oscillation frequency of the LC-tank oscillator 110 approaches one half of the frequency of the injection signal SIN1, the conventional injection-locked frequency divider 100 is in a locked state and a frequency division signal SDI1 is generated. Since the LC-tank oscillator 110 has a high oscillation frequency, the conventional injection-locked frequency divider 100 is applicable in a high-speed system. However, since the LC-tank oscillator 110 cannot provide a wide oscillation frequency range, the locking range of the conventional injection-locked frequency divider 100 is limited, thereby affecting the application range of the conventional injection-locked frequency divider 100 in practice.
FIG. 2 is a schematic structural view of another conventional injection-locked frequency divider. Referring to FIG. 2, the conventional injection-locked frequency divider 200 is constructed by an LC-tank oscillator 210 and a signal injection unit 220. Similarly, the signal injection unit 220 also receives an injection signal SIN2. The LC-tank oscillator 210 adjusts its oscillation frequency through a reactance control signal SIP2. When the oscillation frequency of the LC-tank oscillator 210 approaches one half of the frequency of the injection signal SIN2, the conventional injection-locked frequency divider 200 is in the locked state and a frequency division signal SDI2 is generated. However, in high-frequency operation, an injection current I2 is diminished by the parasitic capacitance in the signal injection unit 220. Therefore, in practical application, the signal injection unit 220 must provide a larger injection current I2 to maintain the primary characteristics of the conventional injection-locked frequency divider 200.
FIG. 3 is a schematic structural view of still another conventional injection-locked frequency divider. Referring to FIG. 3, the conventional injection-locked frequency divider 300 comprises an LC-tank oscillator 310, a signal injection unit 320, and a current-limiting unit 330. Similarly, in a locked state, the injection-locked frequency divider 300 generates a frequency division signal SDI3 through the LC-tank oscillator 310. In order to solve the defects of the conventional injection-locked frequency divider 200, the conventional injection-locked frequency divider 300 receives an injection signal SIN3 through the signal injection unit 320. In another aspect, under the circumstance that an injection current I3 is controlled by the current-limiting unit 330, the power consumption of the conventional injection-locked frequency divider 300 is efficiently limited. The LC-tank oscillator 310 adjusts its oscillation frequency through a reactance control signal SIP3 and the current-limiting unit 330 adjusts and controls the injection current I3 according to a bias current control signal SBI3. However, the conventional injection-locked frequency divider 300 still has the problem of a narrow locking range.
In view of the above, in the practical application, the conventional injection-locked frequency divider has the problems of narrow locking range and high power consumption. In other words, the conventional injection-locked frequency divider cannot be widely used in various mixed signal integrated circuits due to such problems.